alltransretinal

All-trans-retinal, also called all-trans-retinaldehyde, is the aldehyde form of vitamin A and the all-trans isomer of retinal (chemical formula C20H28O). It functions as a chromophore in vertebrate vision and is involved in the visual cycle that regenerates light-sensitive pigments.

In phototransduction, light absorption by rhodopsin converts 11-cis-retinal to all-trans-retinal, triggering a conformational change that starts the neural signal. The all-trans-retinal is released from opsin and rapidly reduced to all-trans-retinol by retinal dehydrogenases to prevent accumulation of reactive aldehyde species. All-trans-retinol is transported to the retinal pigment epithelium, where it is re-esterified and processed by the visual-cycle enzymes, notably RPE65, to regenerate 11-cis-retinal, which is then shuttled back to photoreceptors to reform rhodopsin.

All-trans-retinal is lipophilic and reactive, and free aldehyde can form adducts with proteins and lipids. Healthy retinas employ detoxification and transport systems to minimize buildup, including enzymatic reduction and transporter-mediated clearance. Disruptions in the visual cycle or defects in transporters such as ABCA4 can lead to accumulation of all-trans-retinal and toxic byproducts (for example, lipofuscin and A2E) that are associated with retinal degeneration and diseases such as Stargardt disease. All-trans-retinal thus occupies a central, tightly regulated role in the regeneration of visual pigments and in maintaining retinal health.